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From: James Van Buskirk on 5 May 2008 14:32
I was trying to use the C preprocessor for a Fortran program and it
gave me some insight as to why they are always so out of sorts on
comp.lang.c:

C:\gfortran\clf\cpp>type cpp.f90
module mod1
implicit none
intrinsic SYMBOL_1
end module mod1

module mod2
use mod1, only: fun => SYMBOL_1
implicit none
character(*), parameter :: name = #SYMBOL_1
end module mod2

program test
use mod2
implicit none
real x

x = 3
write(*,'(a,f0.6,a,f0.6)') name//'(',x,') = ',fun(x)
end program test

C:\gfortran\clf\cpp>gfortran -x f95-cpp-input -D SYMBOL_1=BESSEL_J0
cpp.f90 -ocp
p
cpp.f90:9.36:

character(*), parameter :: name = #BESSEL_J0
1
Error: Expected an initialization expression at (1)

I found the -x f95-cpp-input command-line option at

http://gcc.gnu.org/onlinedocs/gfortran/Preprocessing-and-conditional-compilation.html#Preprocessing-and-conditional-compilation

And at

http://gcc.gnu.org/onlinedocs/gcc/Preprocessor-Options.html#Preprocessor-Options

the -D name=#BESSEL_J0 option. At

http://en.wikipedia.org/wiki/C_preprocessor#Quoting_macro_arguments

we find that #BESSEL_J0 should be replaced by "BESSEL_J0" but
upon examination of compiler output we find that it doesn't work.
Also it fails for ifort:

C:\gfortran\clf\cpp>ifort /Qcpp -D SYMBOL_1=ERFC cpp.f90
Intel(R) Fortran Compiler for Intel(R) EM64T-based applications, Version 9.1
Build 20061104
Copyright (C) 1985-2006 Intel Corporation. All rights reserved.

cpp.f90(9) : Error: Invalid radix or character in constant out of radix
range
character(*), parameter :: name = #ERFC
-------------------------------------^

Now we can work around this for gfortran as follows:

C:\gfortran\clf\cpp>type cpp1.f90
module mod1
implicit none
intrinsic SYMBOL_1
end module mod1

module mod2
use mod1, only: fun => SYMBOL_1
implicit none
character(*), parameter :: name = '&
&SYMBOL_1&
&'
end module mod2

program test
use mod2
implicit none
real x

x = 3
write(*,'(a,f0.6,a,f0.6)') name//'(',x,') = ',fun(x)
end program test

C:\gfortran\clf\cpp>gfortran -x f95-cpp-input -D SYMBOL_1=BESSEL_J0
cpp1.f90 -oc
pp1

C:\gfortran\clf\cpp>cpp1
BESSEL_J0(3.000000) = -.260052

But ifort's preprocessor is smart enough to grok a free-form character
continuation context:

C:\gfortran\clf\cpp>ifort /Qcpp -D SYMBOL_1=ERFC cpp1.f90
Intel(R) Fortran Compiler for Intel(R) EM64T-based applications, Version 9.1
Build 20061104
Copyright (C) 1985-2006 Intel Corporation. All rights reserved.

Microsoft (R) Incremental Linker Version 8.00.40310.39
Copyright (C) Microsoft Corporation. All rights reserved.

-out:cpp1.exe
-subsystem:console
cpp1.obj

C:\gfortran\clf\cpp>cpp1
SYMBOL_1(3.000000) = 0.000022

So I ultimately abandoned this C preprocessor nonsense and used
other methods to insert minor edits into my code.

--
write(*,*) transfer((/17.392111325966148d0,6.5794487871554595D-85, &
6.0134700243160014d-154/),(/'x'/)); end


From: glen herrmannsfeldt on 5 May 2008 15:00
James Van Buskirk wrote:

> I was trying to use the C preprocessor for a Fortran program and it
> gave me some insight as to why they are always so out of sorts on
> comp.lang.c:
(snip)

> character(*), parameter :: name = #SYMBOL_1

The processing of #SYMBOL_1 is only done for macro arguments,
so, for example from the indicated web page:

#define QUOTEME(x) #x

The argument of the QUOTEME macro will be quoted when the
macro is expanded. You might try something like:

#define charparm(x) character(*), parameter :: name=#x

In which case charparm(SYMBOL_1) should generate the appropriate statement.

-- glen

From: glen herrmannsfeldt on 5 May 2008 15:07
James Van Buskirk wrote:

> I was trying to use the C preprocessor for a Fortran program and it
> gave me some insight as to why they are always so out of sorts on
> comp.lang.c:

Preprocessor quoting is used in C for debugging expressions such as:

#define dumpme(x,fmt) printf("%s:%u: %s=" fmt,__FILE__,__LINE__, #x, x)

In addition, the compiler will concatenate adjacent string
constants. Maybe:

#define dumpme(x) print *, __FILE__, __LINE__, #x, x

a little more complicated to allow a format descriptor in the macro.

-- glen

From: glen herrmannsfeldt on 5 May 2008 15:20
glen herrmannsfeldt wrote:

> James Van Buskirk wrote:

>> I was trying to use the C preprocessor for a Fortran program and it
>> gave me some insight as to why they are always so out of sorts on
>> comp.lang.c:

> #define dumpme(x) print *, __FILE__, __LINE__, #x, x

In addition, note that # quoting is part of the ANSI preprocessor.

That traditional cpp, which as I understand it is normally used
for Fortran, will expand macro arguments inside quotes. That is,

#define dumpme(x) print *, __FILE__, __LINE__, "x=", x

Note that applies to macro arguments only, not to preprocessor
symbols in general.

-- glen

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